[Music] hi and welcome back to free science lessons. co.uk by the end of this video you should be able to describe how to make a soluble salt by using an acid this is a required practical so it's highly likely that there'll be a specific question on this in your exam we're going to start by recapping what's meant by ass salt and how we make these here's an example of ass salt this is copper sulfate remember that all salts contain a positive ion in this case the positive ion is the metal ion cu2+ this can come from four different chemicals firstly the metal ion could come from the metal itself in this case copper however I should point out that we cannot make copper sulfate by reacting copper with dilute sulfuric acid that's because copper is not reactive enough for that reaction to take place the metal ion could also come from a metal oxide in this case copper oxide it could come from a metal hydroxide in this case copper hydroxide or finally the metal ion could come from a metal carbonate in this case copper carbonate salts also contain a negative ion and this comes from the acid in this case the negative ion is the sulfate ion s so42 minus and to make this we need to to use sulfuric acid so in this video we're going to look at the actual steps involved in making pure crystals of a soluble salt such as copper sulfate I'm showing you copper sulfate crystals here now according to the AQA specification you need to know how to carry out this practicle using either a metal oxide or a metal carbonate so we're only going to look at these we're going to look at the reaction between solid copper oxide and dilute sulfuric acid but these stages would equally apply to making a salt using a metal carbonate such as copper carbonate I'm showing you copper oxide here as you can see it's a black powder so here's the equipment that we're going to use for the first stage which is making the soluble salt first we start with a fixed amount of dilute sulfuric acid this is our limiting reactant in other words the acid will run out now this is really important we do not want any acid remaining at the end as that would contaminate our salt so we need to make certain that all of the acid is reacted away now we gently heat the acid until it's almost boiling however we do not want it to boil as it could bubble over when we add our other reactant and that would be dangerous now using a spatula we add small amounts of copper oxide to the acid we then stir the solution using a glass rod the copper oxide will react and seem to disappear this solution will turn a blue color which is a color of copper sulfate continue adding copper oxide if the solution continues to be clear blue stop adding copper oxide if some powder remains after stirring now at this point the reaction has stopped as all of the acid has reacted we've made copper sulfate and the solution is now neutral in the next step we're going to make crystals of our copper sulfate but first we need to remove the unreacted copper oxide because this is insoluble we can filter it away to do this we use a filter funnel and filter paper which I'm showing you here now in the final stage we need to make crystals of our salt and to do this we use evaporation so we're going to look at that now we take our copper sulfate solution and place this in an evaporating Basin like this we then heat this gently over a beaker of boiling water we need to heat this until around half the solution remains at this point we leave the solution for 24 hours in a cool place for copper sulfate crystals to form finally we scrape the copper sulfate crystals on a paper towel and we gently Pat them dry now we have pure dry crystals of our copper sulfate remember you'll find plenty of questions on this required practical in my vision workbook and you can get that by clicking on the link above okay so hopefully now you should be able to describe how to make a soluble salt by using an [Music] acid